HISTORICAL LOSS AND LAE DEVELOPMENT - Environmental, Asbestos and Mass Tort Exposures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
ENVIRONMENTAL, ASBESTOS AND MASS TORT EXPOSURES
Current accident year	$ 364,472	$ 361,451	$ 332,282
Unpaid losses and LAE at end of year:
Gross	1,103,785	1,121,040	1,129,433	$ 1,158,483
Ceded	(297,844)	(335,106)	(354,924)	(359,884)
Net	805,941	785,934	774,509	$ 798,599
Environmental, Asbestos and Mass Tort Claims
Loss and LAE payments (cumulative)
Gross	119,632	112,819	105,559
Ceded	(62,463)	(59,376)	(57,976)
Net	57,169	53,443	47,583
Unpaid losses and LAE at end of year:
Gross	41,062	39,064	48,507
Ceded	(12,559)	(11,879)	(15,043)
Net	$ 28,503	$ 27,185	$ 33,464
Minimum period for which product lines related to majority of reserves have been in runoff	20 years
1983 AEMT Claim
Unpaid losses and LAE at end of year:
Gross increase in loss	$ 2,500
Net increase in loss	$ 2,400